The present invention relates to an optical system whose magnification ratio is variable, particularly an optical system in accordance with which the attachment lens is mountable in and dismountable from the optical path.
When a scene is observed in the case of a single lens reflex camera, the photographer looks through the eye piece lens arranged in the prism housing of the camera body. Accordingly, when the scene is observed along the direction at a right angle to the optical axis of the photographing lens, with the eye kept apart from the camera body, an angle form finder is used. The angle finder is provided with a mirror or a reflecting plane of the prism in the optical path of the finder so as to bend the optical path. Recently, the magnification ratio has been made variable.
In the Japanese Utility Model Application Nos. Sho 51-152337(1976) and Sho 52-133632(1977) an angle finder is disclosed whose magnification ratio is variable by mounting a Galilean optic consisting of a positive lens and a negative lens in front of the objective lens in the finder optical system or dismounting the Galilean optics from the objective lens. In the case of Sho No. 51-152337, the Galilean optic is rotated around the axis vertical to the optical axis in such a manner that the light travels between the positive and the negative lens so as to lower the magnification ratio. In the case of Sho No. 51-133632, a Galilean optic is secured on a turret which rotates around an axis parallel to the optical axis so as to mount or dismount the Galilean optic by rotating the turret.
On the other hand, the variable magnification lens system in accordance with the present invention can be applied to the telescope or the binoculars.